Interface advance control in secondary recovery program by reshaping of the interface between driving and driven fluids and by the use of a dynamic gradient barrier

ABSTRACT

The interface between driving and driven fluids in a secondary recovery operation is reshaped after a cusp has developed by injection of a fluid via wells controlling the flow gradients, and the arrival of the injected driving fluid into the vicinity of a production well is delayed by the imposition of a dynamic gradient barrier of produced formation fluids.

United States Patent Hoyt 5] June 27, 1972 s41 INTERFACE ADVANCE CONTROL IN [56] References Cited SECONDARY RECOVERY PROGRAM UNITED STATES PATENTS BY RESHAPING OF THE INTERFACE BETWEEN DRIVING AND DRIVEN R24,873 9/1960 Lindauer ..l66/268 FLUIDS AND BY THE USE OF A 3,074,481 1/ 1963 Habermann... 3,109,487 11/1963 Hoyt ..166/245 DYNAMIC GRADIENT BARRIER 3,135,325 6/1964 Parker ..166/266 [72] Inventor: Donald L. Hoyt, Houston, Tex. 3,215,198 1 1/1965 willman ..l66/263 73 T N k 1 Asslgnee exam Inc ew Yor N Y Primary Examiner-Stephen J. Novosad Filedl 1970 AttorneyCarl G. Ries, Thomas H. Whaley and Joseph 211 Appl. No.: 102,815 Daleda Related US. Application Data ABSTRACT [63] Continuation-impart of Ser. Nos. 786,565, Dec. 24, The interface between driving and driven fluids in a secondary 1968, Pat. No. 3,592,265, and Ser. No. 786,568, Dec. recovery operation is reshaped after a cusp has developed by 24, 1968, Pat. No. 3,593,787. injection of a fluid via wells controlling the flow gradients, and the arrival of the injected driving fluid into the vicinity of a [52] U.S.Cl ..l66/245 r d ti ll is d layed by the imposition of a dynamic [51 1 Intgradient barrier of produced fo nation fluids [58] Field of Search ..166/245, 268, 273-275 16 Claims, 13 Drawing Figures 25 6a a e3 f/VD P/flJfZ PATENTEDJum m2 SHEET 2 OF 3 NMNQQQQ 93% PATENTEDJUNN m2 SHEET 3 OF 3 .w .m aw Jaw 5 E 1 5m msm 4 3 INTERFACE ADVANCE CONTROL IN SECONDARY RECOVERY PROGRAM BY RESHAPING OF THE INTERFACE BETWEEN DRIVING AND DRIVEN FLUIDS AND BY THE USE OF A DYNAMIC GRADIENT BARRIER CROSS REFERENCES This application is a continuation-in-part application for patent of the copending, commonly assigned applications for patent, Ser. No. 786,565, filed Dec. 24, 1968 by Donald L. Hoyt for Interface Advance Control in Secondary Recovery Program by Reshaping of the Interface Between Driving and Driven Fluids, now U.S. Pat. No. 3,592,265, and Ser. No. 786,568, filed Dec. 24, 1968 by Donald L. Hoyt for Interface Advance Control in Secondary Recovery Program by Use of Gradient Barrier, now U.S. Pat. No. 3,593,787.

FIELD OF THE INVENTION This invention relates generally to the production of hydrocarbons from underground hydrocarbon-bearing formations, and more particularly, to a method for increasing the efficiency of the production of hydrocarbons therefrom by controlling the advance of the interface in pattern floods.

DESCRIPTION OF THE PRIOR ART In the production of hydrocarbons from permeable underground hydrocarbon-bearing formations, it is customary to drill one or more wells into the hydrocarbon-bearing formation and produce hydrocarbons, such as crude oil, through designated production wells. Sooner or later, the flow of hydrocarbon-bearing fluids diminishes and/or ceases, even though substantial quantities of such fluids are still present in the underground formations.

Thus,secondary recovery programs are now an essential part of the overall planning for virtually every crude oil and gas-condensate reservoir in underground hydrocarbon bearing formations. In general, this involves injecting an extraneous fluid, such as water or gas, into the reservoir zone to drive formation fluids including hydrocarbons toward production wells by the process frequently referred to as flooding. Usually, this flooding is accomplished by injecting through wells drilled either in a geometric pattern, the most common pattern being the five-spot, or in line.

When the driving fluid from the injection well reaches the production wells of a five-spot pattern, the areal sweep is about 71 percent. By continuing production considerably past breakthrough, it is possible to produce much of the remaining unswept portion. When the driving fluid from a line of injection wells in a line drive reaches the first line of production wells, the areal sweep is about 53 percent. By standard procedure, it is possible to obtain about 90 percent sweep but with the attendant problem of the separation and disposition of excessive quantities of driving fluid. It would be a great economic benefit to be able to achieve a sweep of 100 percent of the hydrocarbon-bearing formation. It would be an even greater benefit to be able to achieve it at breakthrough, so that it would not be necessary to produce large quantities of injected driving fluid.

It is understood that the failure of the driving fluid in secondary recovery operations to contact or sweep all the hydrocarbon area is due to the development of a cusp at the. interface between the driving and the driven fluids which advances toward the production well. If other portions of the interface could be made to keep up, or if the cusp formation were delayed, a more complete areal sweep would be possible.

One aspect to increase the sweep is disclosed in the commonly assigned U.S. Pat. No. 3,393,734, issued to BL. Hoyt et al. on July 23, 1968 and involves the retardation of the development of the cusp toward a production well. The method of achieving more uniform advance is to control the flow gradients so that the interface is spread out. This can be done either by choosing a particular geometry of well positions or by adjusting the relative production rates so that the velocity of advance is not predominantly in one direction. It

can be done also by shifting the gradients frequently, in both direction and magnitude, thus preventing any one section of an interface from advancing too far out of line.

In the commonly assigned U.S. Pat. No. 3,393,735, issued to A.F. Altamira et al. on July 23, 1968 for Interface Advance Control in Pattern Floods by Use of Control Wells, there is disclosed how an increased amount of hydrocarbons is produced from an underground hydrocarbon-bearing formation by employing at least three wells, penetrating such a formation, which wells are in line, to produce hydrocarbons from the formation via two of these wells including the middle well, as disclosed in the commonly assigned U.S. Pat. No. 3,109,487, issued to Donald L. Hoyt on Nov. 5, 1963 for Petroleum Production by Secondary Recovery. In both these cited patents, there is disclosed how a production control well is positioned between the injection well and the production well and is kept on the production after the injected fluid reaches it. In this manner, the cusp is pinned" down at the control well and while the area swept out by the injection fluid before breakthrough at the outer production well is increased, there is an unwanted handling of considerable quantities of injected fluid at the control well.

SUMMARY OF THE INVENTION It is an overall object of the present invention to provide an improved secondary recovery procedure involving initially at least two production wells substantially in line with a source of driving fluid (such as an injection well or active aquifer), which wells may be part of a well arrangement for exploiting a hydrocarbon-bearing formation, by reshaping the interface between a driving fluid and formation fluids, after development of a cusp, into a configuration favorable to greater sweep, thereafter providing a dynamic barrier between the injection well and a production well, by changing the function of the wells at strategic times to gain maximum control of the flood front.

Such a well grouping is arranged with three wells substantially in line so that an end well in line is completed for injection and the remaining two wells are completed for production. Flooding is initiated at the end well by injection thereinto of an extraneous driving fluid, such as water or gas, and proceeds until breakthrough of the flood front occurs at the closer of the production wells in line at which time injection of driving fluid via the end well to maintain flooding is suspended, the production well or wells are put on a standby basis, and a small volume of an extraneous fluid is injected into the formation via the production well at which breakthrough occurred, to drive the cusp of the flood front therefrom and reshape the interface for the next production phase. Examples of the extraneous fluid include produced formation hydrocarbon fluids, which may be treated with thickeners to increase the viscosity thereof, butane and propane, all being miscible with the formation fluids. Reshaping of the interface can be started at a predetermined time prior to breakthrough also. Then, injection is resumed at the end well and production is continued (or initiated) at the other or outer production well and additional extraneous fluid is injected continuously at low rate into the production well suffering breakthrough to provide a dynamic barrier.

The interface has now been reshaped so that instead of just one point, viz. the tip of the cusp, being closest to the outer production well and thereby being accelerated to early breakthrough by the radial flow gradients, all the points over an appreciable portion of the interface will now be approximately equal travel time away from the outer production well, this travel time being greater than would have been the time for breakthrough without injection of the extraneous fluid via the production well sufiering breakthrough. In addition, the flanks of the flood front are reshaped, by being advanced during the initial period of injection of the extraneous fluid. Thus, more of the less accessible areas are swept, and the reversal of the cusp, coupled with the dynamic barrier created by the continuously cycling extraneous fluid, allows more sweep before breakthrough of the driving fluid into the outer production well.

Upon continuing the injection of the extraneous driving fluid via the end well and extraneous fluid via the converted production well and the production of formation fluids, the flood front will cusp eventually into the other production well in line at which time injection of the extraneous fluids is suspended and the production well is put on a standby basis.

If recovery of the extraneous fluid is desired, production of formation fluids along with the extraneous fluid and extraneous driving fluid may be continued from the production well for a predetermined period.

A preferred procedure, if it is desired to recover the injected extraneous fluid, is to cease the continuous injection which supports the dynamic barrier at a time when the driving fluid is nearing, but has not yet reached, the production well. The optimum condition exists when the interface, moving around the dynamic barrier, has advanced to between onethird and two-thirds of the distance from the converted well to the next production well on line. This condition can be calculated from observed rate of interface advance, or inferred from rise in ratios of produced fluids. The described procedure allows substantially all of the extraneous fluid to be recovered at the time of breakthrough of extraneous driving fluid into the production well.

With a line drive, other production wells undoubtedly would be aligned with the injection well and two production wells, and to continue the production, the injection of driving fluid is suspended while a small volume of an extraneous fluid is injected into the formation via the production well at which breakthrough has just occurred. This injection of extraneous fluid will drive the cusp back and modify the interface for the next production phase. Then injection of extraneous driving fluid via the end well or the converted production well is resumed and injection of extraneous fluid via the next converted well is initiated and production is resumed.

The continuous injection into the converted well establishes a system of pressure gradients which on one side of the well are directed opposite to the pressure gradients associated with the driving fluid. A point of equilibrium of forces is established wherever the components of pressure gradient directed away from the converted well are equal and opposite to the components directed toward that well. The locus of all such equilibrium points establishes a stable interface, normally teardrop shaped, around the converted well. The shape and size of this interface will depend upon the interrelationship of many factors, primarily, geometry of well positions, relative permeabilities and viscosities, and well rate distributions. Control of any of these factors can be used thereby to enhance the effectiveness of the method to create a gradient barrier.

Since the injected driving fluid cannot penetrate this gradient barrier, it must travel a roundabout and longer flow path to reach the further production well, thereby delaying cusping into the end in line production well and allowing a longer period for the advance of the interface between the driving fluid and the formation fluids before breakthrough at this futher production well. When production at this end well is continued after breakthrough, the converted well is shut in and the continuing production results in recovery of the injected produced formation fluids, along with remaining in place formation fluids.

Many variations of this basic procedure are possible, and some will be more advantageous than others for particular geometries of well positions, and reservoir and fluid parameters. But they will have certain things in common:

1. An intermediate well between and in the line through an injection source and a production well either exists or is added:

2. At breakthrough into this intermediate well or some time prior thereto, the injection of driving fluid is suspended and a volume of fluid, such as a portion of the produced hydrocarbon fluids, is injected into the well suffering breakthrough.

This injection is done without simultaneous production from other wells to reshape the interface at the breakthrough well;

3. Injection of driving fluid is resumed at the initial injection well and production is initiated or resumed at another well, and injection of an extraneous or barrier fluid is continued into the well sufi'ering breakthrough at a rate equal to a percentage of the production rates to provide a dynamic gradient barrier;

4. This continues, even though other existing wells may be captured by injected driving fluid and closed in, until breakthrough of the injection fluid into the production well on the other side of the converted well;

5. At this time, or in some cases even before it, the injection of barrier fluid is stopped, and continued injection of driving fluid on one side and continued production on the other will move the barrier fluid completely into the production well if recovery of this fluid is desired (as, for example, if the barrier fluid used comprises produced hydrocarbon fluids).

Other objects, advantages and features of this invention will become apparent from a consideration of the specification with reference to the figures of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is illustrative of the interface advance in the form of a cusp toward a corner production well in one quadrant of an inverted five-spot pattern undergoing secondary recovery (Prior FIG. 2 discloses one unit (Prior Art);

FIG. 3, corresponding to FIG. 2, discloses one quadrant of a nine-well diagonal pattern, illustrating cusp development at an interior production well, P, (Prior Art);

FIG. 3a discloses one quadrant of a nine-well diagonal pattern, illustrating the reshaping of the cusp at an interior control well between the injection well and the corner production well resulting from injection of a small volume of produced hydrocarbon fluids into such a control well, with all other wells temporarily shut in;

FIG. 3b discloses the same quadrant of a nine-well diagonal pattern, illustrating the breakthrough at a corner production well, P following the provision of a dynamic barrier at the interior control well between the injection well and the corner production well resulting from continuous injection of a small percentage of produced formation fluids into such a control well;

FIG. 3c discloses the same quadrant of a nine-well diagonal pattern, illustrating the final production of the injected produced formation fluids;

FIG. 4 illustrates a line drive of at least three wells wherein the cusp interface is reshaped at the first line production well and a dynamic barrier is imposed thereon. Thereafter and as each of the in line production wells in turn suffers breakthrough this dual step process is repeated;

FIG. 5a, 5b and 5c and 6a, 6b and 6c, illustrate the changes in well functions in accordance with the movement of the interface as a result of cusp reshapings and dynamic barriers imposed on it during the several phases of the production program, respectively, in a 13-well grouping and 17-well grouping undergoing secondary recovery.

The objects of the invention are achieved by the use of a combination of production wells used as control wells to modify the interface of injected driving fluid and to delay, by a dynamic barrier, its advance into the outermost production wells, thereby obtaining more sweep and recovery of formation hydrocarbons before breakthrough of the driving fluid.

The specification and the figures of the drawings schematically disclose and illustrate the practice and the advantages of the invention with well patterns and/or groupings and areal sweep examples which are obtainable and have been observed both in secondary recovery operations and in potentiometric model studies indicate a sweep obtained in an ideal reservoir, although the recovery from an actual sweep of a particular field may be more or less, depending on field parameters.

of a nine-well diagonal pattern Throughout the figures of the drawings, the same symbols will be maintained as follows: I is the central injection well, P,, P,, and P, represent respectively production wells at the corners, along the sides, and the interior control wells of the pattern or well arrangement; the left diagonal represents the reinjected produced formation fluids; and, a solid circle indicates a production well, a crossed circle indicates a shut in well, an open circle a well site, an upwardly arrowed open circle indicates an injection well, and a downwardly arrowed solid circle, a converted well. The diagonal x--x in FIGS. 5a and 6a represents an axis of an injection well and a pair of in line production wells.

FIG. 1 illustrates the growth of the cusp in one quadrant of an inverted five-spot pattern unit, wherein the secondary flooding or driving fluid is injected into the central well and production is maintained at the comer wells (of the complete unit) until breakthrough, to result in an areal sweep of approximately 71 percent.

Referring to FIG. 2, there is disclosed the basic pattern unit of a nine-well diagonal pattern, essentially the five-spot pattern with control wells positioned on the diagonals between the central injection well and the comer production wells. The control wells should be spaced at least one-half the distance between the injection well and each corner production well, with the best results obtained when such control wells are positioned between three-quarters and seven-eighths of the distance from the injection well toward the corner production wells. With such a pattern, the invention disclosed in the cited patent to Hoyt can be employed with success to increase the sweep area over that mentioned for the basic five-spot pattern.

Use of control wells as disclosed by the above-cited patents to Hoyt and to Altamira et a1, by continuing production from P, after breakthrough even to 100 percent injected fluid, will have a beneficial effect but at the cost and difficulty of han-. dling and disposing of large quantities of the driving fluid.

Instead, if a small volume of produced formation hydrocarbon fluids, e.g. about percent of the pore volume of a quadrant of a pattern unit illustrated in FIG. 3a, is injected into the formation via each control well, P,, from which production has ceased, each cusp will be reshaped by being driven back, and flank portions of the interface or flood front will be advanced (as indicated by the looped line A,,-A in FIG. 3a), by the injected bubble of produced formation hydrocarbon fluids, shown in section with left diagonals in outline D,.

Should production be initiated at the corner well, P with P, shut in, and injection of extraneous driving fluid resumed at the central well, I, the interface and bubble both move toward the production well, P Now, however, all the points between a and c on the interface are approximately the same travel time from P and as the flood front progresses, the bubble is re-produced and the points between a-c converge into the production well, yielding at breakthrough, a sweep of 87 percent. The advantage of high sweep is thereby realized without handling injection fluid.

If satisfactory production of reservoir fluid along with injection fluid is possible in a given reservoir, (it often is not), this percentage can be increased by continued production.

The improvement in sweep can be optimized in several ways. The size of the bubble, the geometry of the wells, the relative rate distribution and judicious use of the central injection well during the reshaping phase, can be used in any given operation to mold the interface into the best shape for the next production phase.

In FIG. 3b, the invention illustrates the improvement provided by the embodiment of this invention over the disclosures of the prior art. In the prior art, with injection of the driving fluid via the central well of a nine-well diagonal grouping, production is maintained via the interior control well, P,, (or also via the comer production well, P until breakthrough thereat, to yield a sweep of 57 percent. The control well, P,, is located on the diagonal through the injection well and the comer production well, P about three quarters of the distance from the central injection well, I. If the production well at P, were shut in to avoid handling any of the injected driving fluid and production were initiated (or continued) and maintained till breakthrough at the comer well, P the sweep (not indicated) would increase by 9 percent, for a total sweep of 66 percent.

However, if as shown in FIG. 3a, a volume of produced formation hydrocarbon fluids equal to a predetermined amount, e.g. about 15 percent of the pore volume of a pattern unit, is injected through the interior control wells, P,, from which production has ceased, and the cusp reshaped by being driven back by the resulting injected bubble of produced formation hydrocarbon fluids, as shown in section with left diagonals at D,, the interface is distorted as indicated by the loop outline with the point of the cusp being driven back from the control well, P,, to form the interface at a-c, FIG. 3a while the flanks advance.

When production is initiated (or resumed) at the corner well, P and with about 50 percent of produced formation fluids being injected continuously into the formation via well P,, the cycling formation fluids form a stable teardrop bubble, as indicated in left diagonal sectioning at D FIG. 3b. The envelope of this bubble represents the surface of equilibrium of pressure gradient forces, and acts as a gradient barrier.

By the time the driving fluid gets around the gradient barrier to achieve breakthrough at the corner production well, P the sweep of the formation fluids has been increased 31 percent, for a total sweep of 88 percent.

Finally, if production at P is continued after breakthrough with the control well P, closed in, as illustrated in FIG. 30, maximum gradients are reestablished along the axis of the wells, and virtually all the injected produced formation fluids can be recovered quickly, as indicated in FIG. 30, along with additional formation fluids miscible therewith, bringing total sweep to over 90 percent before an appreciable percentage of injected driving fluid is produced.

The sweep can be increased either by forming a larger initial bubble or using a greater fraction of the produced formation fluids for injection back into the formation via the converted control well.

FIG. 4 illustrates phases of an in line production drive wherein a predetermined amount of produced hydrocarbon fluids is injected, as indicated by the left diagonal section lines at C, (as the second phase to reshape the cusp and form the interface at a, b, c, d) into the formation via the well P at which breakthrough of the driving fluid, injected as the first phase via the injection well in line, I, has occurred. The prior art discloses about a 53 percent areal sweep at the end of the first phase, and when production is continued after breakthrough a 90 percent sweep can be obtained but with the attendant problem of handling and disposal of driving fluid.

During the third phase, comprising injection of extraneous driving fluid into the injection well, I, and the continuous injection of a portion of produced formation fluids via well P the shape of the injected formation fluids changes to the stable teardrop shape indicated by left diagonals in section C,, with the same amount of these fluids being both continuously reproduced from P,, and continuously reinjected into P while the interface between the formation fluids and the extraneous driving fluid, ab and cd, advances around each side of the dynamic barrier toward the production well P When the driving fluid-formation fluid interface has reached a point between one-third and two-thirds of the distance from P,,, to P,,- as indicated by observation or calculation from field and fluid properties, the fourth phase is initiated by shutting in P,,. This allows the flow gradients to re-orient themselves such that the maximum velocity will now be along the line of the wells, and the reinjected fluid will be swept toward the well P 2 as the driving fluid advances, as indicated by the section C Ideally, at breakthrough of driving fluid, virtually all of the reinjected fluid will have been recovered, although it is possible that some small volume may still be unrecovered, as illustrated at end of phase 4.

At the end of this phase, the production well P is converted into an injection well for produced formation fluids to reshape the interface as in the second phase, with injection of extraneous driving fluid via well P being initiated and well I being shut in. Succeeding phases follow in same order. Although the sweep is the same as in the prior art, less driving fluid is required, there are no handling and disposal problems, and the operation is done in one half to one third the time.

FIGS. a, 5b and 5c disclose the basic nine-spot pattern modified by the addition of four interior control wells, which can be positioned along the diagonals of the pattern for best advantage as indicated previously. It can be visualized also as a four unit five-spot pattern, wherein the injection wells of the inverted five-spot pattern units have been converted to production wells, and the innermost production well of the four unit five-spot pattern has been converted into an injection well. With such a conversion, the positions of the control wells have been predetermined and may not be situated for best effect.

As illustrated in one quadrant of this l3-well grouping, the first phase of the production method requires injecting driving fluid via the central well and production initiated and maintained at the diagonal wells of the pattern until breakthrough is achieved at the four interior control wells, as shown by the dash outline in FIG. 5a as the end of phase I. Then these interior production wells are converted to injection wells for receiving produced formation hydrocarbon fluids to reshape the cusp as shown by the left diagonals in section B,, FIG. 5a (end of phase 2) and later to provide a dynamic barrier indicated by the left diagonal section B FIG. 5b while production is resumed or initiated from the corner wells P until the end of Phase 3 when the interface between driving fluid and formation fluids is approximately as shown in FIG. 5b. To begin Phase 4, the interior control wells are now shut in and production of formation fluids along with reinjected produced formation fluids is continued from the corner wells until breakthrough thereat by the driving fluid, at which time the reinjected formation fluids would be nearly all recovered, with any unrecovered portion consisting of 'a small lens of such fluids, as illustrated by section B in left diagonals, in FIG. 5b. (End of Phase 4).

If production after breakthrough at the corner wells is continued, it becomes feasible to recover these lenses. This would be accomplished most readily during the final phase, which comprises placing the sidewells P, on production until breakthrough of the driving fluid occurs thereat, (end of Phase 5), at which time a total sweep of 90 percent is obtained, leaving only slivers of unswept areas adjacent the corner production wells.

In FIGS. 6a, 6b and 6c, there is illustrated the several phases of a secondary recovery operation applied to a quadrilateral well grouping having interior control wells and side wells, specifically as shown, to a l7-well grouping, wherein the production occurs consecutively along the diagonals, to accomplish substantially the same sweep, as in the simultaneous diagonal production illustrated in FIGS. 5a, 5b and 50.

In FIG. 6a, there are illustrated the first two phases of diagonal production with the opposite comer wells and side wells on a standby-basis, i.e. shut in. At the end of the first phase, the extraneous driving fluid from injection well I has caused a breakthrough at the interior control wells P and the end of phase 2 illustrates the reshaping of the cusp by the injection of a predetermined volume of produced hydrocarbon fluids, indicated by the left diagonals in sections E.

In FIG. 6b, a dynamic barrier has been imposed by the continuous injection of a predetermined percentage of produced formation fluids via the production wells suffering breakthrough, viz. P with the end of Phase 3 occurring upon breakthrough of the extraneous driving fluid at the corner production wells P the dynamic block being indicated by the left diagonal sections at E Phase 4, following, comprises further production after breakthrough to recover all or most of the reinjected produced formation fluids, any unrecovered portion remaining as a small lens at the corners as indicated at E The additional sweep caused by continued advance of the flanks of the interface during the phase is not shown for purpose of clarity. Phase 5, similar to phase 1, begins by shutting in the wells on this diagonal and initiating production along the other diagonal, with the side wells still shut in. The end of Phase 5 occurs upon breakthrough at the production wells P and the cusp is then reshaped, as before, by the injection of a predetermined volume of produced hydrocarbon fluids indicated at E, in FIG. 60, as the end of Phase 6, similar to Phase 2.

Phase 7, corresponding to Phase 3, establishes the dynamic barrier by continuous reinjection of a percentage of the produced formation fluids into P and continues the injection of driving fluid into I, and ends upon breakthrough of the driving fluid into the corner production wells P The dynamic barrier is indicated as IE but not drawn in and sectioned as in FIG. 6b, for clarity.

As in Phase 4, Phase 8 consists of re-production of the reinjected fluid, and ends with recovery either of all of it, or of all but a small lens of reinjected fluid, E near the corner well.

The last phase, Phase 9, consists of production from the side wells P, until breakthrough, other production wells being on standby, or shut in basis.

In any kind of a secondary recovery operation in which one fluid is moved by another toward what is essentially a point sink, such as a production well, the radial flow gradients in the vicinity of the production well inevitably cause the interface to form a cusp pointing toward that well. The various fluid and field parameters, such as permeability distribution, viscosity ratio, well geometry, types of drives, miscibility, displacement efliciencies, etc., will cause the cusp to form earlier or later and be more or less pronounced, but it will form always, and always it will be detrimental to efficient sweep of any region being considered.

The ideal sweep situation for a reservoir would be one in which the fluid interface, as it approaches the last production well, somehow would be in such a geometrical position that all points on it would require the same time to reach the well. The method of spreading the cusp disclosed in US. Pat. No. 3,394,734 (to Hoyt et al.) is successful because it approaches this ideal.

There will be times, however, when the cusp cannot be spread" out, and the presently disclosed method offers a convenient and workable alternative. All that is required is that there be at least two wells substantially in line with a source of driving fluid such as an injection well or an active aquifer. The principle involved is as follows:

The point of the cusp forms along the line of strongest gradient between the injection source and the nearest production well. If fluid is injected into the production well, which is here called the control well, the system is reversed and the point of the cusp is driven back and away from the next production well in line, by the fluid injected via the control well. The interface between the control well fluid and the injection well fluid becomes concave. If the proper size of bubble is introduced, to fit the particular well geometry, the concavity may be sized such that all or most of the points on it (between a and c, e.g., in FIG. 3a) will be in gradient fields such that their time of travel to the production well will be equal.

Resumption of injection of driving fluid and of production from the well beyond the control well will yield a very high sweep. The wider the distance between points a and c, the greater, in general, will be the sweep at breakthrough of these points into the production well. This distance can be increased if the points of injection should straddle the axis extending through the injection and production wells.

Reservoir hydrocarbons are particularly suitable here for control well injection fluid, since they will follow most closely model study preductions, and will be recovered without difficulty in the subsequent production phase. However, any fluid of properties (particularly viscosity and miscibility) similar to the reservoir fluid can be used effectively.

The effect of continuous injection of a control well fluid into the formation between the well injecting driving fluid and a production well is to create an interior envelope of cycling fluid between the control well and the production well, i.e. a dynamic barrier, which the driving fluid cannot penetrate. This condition forces the driving fluid to move around this barrier thus retarding cusp formation toward the production well, giving longer tine for sweep before interface breakthrough. Clearly, the wider the barrier can be made, the better will be the sweep.

Factors which will cause such a barrier to be wide are:

A. higher viscosity of the control well fluid than of the driving fluid;

B. high control well injection rates as a percentage of production;

C. production from side wells during the control well injection phase;

D. dual control wells straddling the axis through the injection and production wells to form a wider bubble, depending on the spacing between the straddle wells.

Any pattern and/or rate distribution which retards the development, or the advance, of a cusp towards production wells will increase the sweep of a field.

Herein has been disclosed another method of delaying the advance of the interface in the form of a cusp toward a production well by reshaping the cusp interface, either prior to or at breakthrough in combination with locating a dynamic barrier or produced formation fluids between an injection well and the outer production well.

Although emphasis has been placed in this disclosure on the practice of this invention as directed to a secondary recovery operation, particularly employing water or other similar aqueous fluid as the injection displacement or extraneous driving fluid, the advantages obtainable in the practice of this invention are also realized in primary hydrocarbon production operations wherein the hydrocarbon-bearing formation is under the influence of either a water or gas drive, or both a water and gas drive, and also in the instance of a secondary recovery operation wherein a gas, such as natural gas, is employed as the driving fluid. Moreover, the invention is applicable to an arrangement of a pair of production wells in line under the influence of an active water drive.

Although disclosure has been made to the continuous injection of produced formation fluids, depending on conditions, these fluids could be separated and produced hydrocarbon fluids could be used to maintain the dynamic barrier, as well as reshaping the cusp at initial breakthrough.

lclaim:

l. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation which comprises penetrating said formation with at least three wells substantially in line, a first well, a second well and a third well, the second and third wells being on one side of said first well with said second well closer thereto, injecting an extraneous driving fluid into said formation via said first well to displace fluids including hydrocarbons in said formation toward said second and third wells, producing said formation fluids including hydrocarbons from said formation via said second well, recovering formation hydrocarbon fluids from produced formation fluids, ceasing injecting said extraneous driving fluid and ceasing producing said formation fluids via the production well upon or before sufiering breakthrough of said extraneous driving fluid thereat and thereupon injecting a predetermined volume of an extraneous fluid into said formation via said production well suffering breakthrough to reshape the cusp, and thereupon continuously injecting a predetermined portion of the produced formation fluids to provide a dynamic gradient barrier while injecting extraneous driving fluid via said first well and producing formation fluids via said third well until breakthrough of said extraneous driving fluid thereat.

2. In the method as defined in claim 1, upon breakthrough ceasing injecting said produced formation fluids while maintaining producing said formation fluids including hydrocarbons from said formation via said third well.

3. In the method as defined in claim 1, continuing injecting produced formation hydrocarbon fluids via said well suffering breakthrough first for a predetermined period while maintaining producing via the remaining production well.

4. In the method as defined in claim 1, said injecting of said extraneous fluid via said production well suffering breakthrough first being a percentage of the pattern unit volume in the amount of about 15 percent, said extraneous fluid being selected from the group consisting of butane, propane and produced hydrocarbon fluids.

5. In the method of producing formation fluids as defined in claim 1, said three wells in line being part of a thirteen well grouping, wherein the central well of said grouping is an injection well and the remaining grouping wells are production wells arranged equally along the sides and on the diagonals of a quadrilateral, said second and third wells being arranged along a diagonal thereof.

6. In the method of producing formation fluids as defined in claim 5, simultaneously initiating producing said formation fluids via all of said production wells except the side production wells.

7. In the method of producing formation fluids as defined in claim 6, ceasing producing from said production wells upon breakthrough thereat and shutting in each one thereafter, and upon ceasing production from the aforementioned production wells, initiating producing from the side wells until breakthrough thereat.

8. In a method of producing formation fluids including hydrocarbons as defined in claim 1, said wells being part of a direct line drive grouping.

9. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation which comprises penetrating said formation with at least three wells substantially in line, a first well, a second well and a third well, the second and third wells being on one side of said first well with said second well closer thereto, injecting an extraneous driving fluid into said formation via said first well to displace fluids including hydrocarbons in said formation toward said second and third wells, producing said formation fluids including hydrocarbons from said formation via the second well, recovering formation hydrocarbon fluids from produced formation fluids, ceasing injecting said extraneous driving fluid and ceasing producing said formation fluids upon breakthrough of said extraneous driving fluid at a production well and then injecting an extraneous fluid into said formation via said last mentioned well to reshape the cusp of the interface between said driving fluid and said formation fluids and producing said formation fluids including hydrocarbons from said formation via said third well while injecting said extraneous driving fluid into said formation via said first well and continuously injecting said extraneous fluid into the production well suffering breakthrough until breakthrough of said extraneous driving fluid at said third well.

10. In the method as defined in claim 9, said injecting of said extraneous fluid via said production well first suflering breakthrough being of predetermined amounts, starting with a percentage of the pattern unit volume for reshaping of the cusp and continuing with a percentage of the produced formation fluids, while producing said formation fluids from said remaining production well to provide a dynamic gradient barrier therebetween.

11. In the method as defined in claim 9, said extraneous fluid injected via said second well being selected from the group consisting of butane, propane and produced hydrocarbon fluids.

12. In the method of producing formation fluids as defined in claim 9, said three wells in line being part of a seventeen well grouping, wherein the central well of said pattern is an injection well and the remaining pattern wells are production wells arranged in equal numbers along the sides and on the diagonals of a quadrilateral.

13. In a method of producing formation fluids as defined in claim 12, producing formation fluids via the wells located on a first diagonal of said grouping and continuing producing therefrom until breakthrough of said extraneous driving fluid occurs at the production well closer to the injection well, thereupon converting said aforementioned diagonal well into an injection well and injecting into said formation via such converted well an extraneous fluid in the amount of 15% of the pattern unit volume, while ceasing injecting said driving fluid, to reshape the cusp of the interface at said converted well, thereupon resuming injecting said driving fluid and producing from the corner well of said first diagonal while continuously injecting said extraneous fluid into said converted well to provide a dynamic barrier therebetween, until breakthrough of said comer well, thereafter shutting in the production wells on said first diagonal and repeating the procedure on the wells on the second diagonal and thereafter producing from the side wells.

14. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation under the influence of an active aquifer which comprises penetrating said formation with a pair of production wells in line with the direction of advance of said aquifer, producing formation fluids including hydrocarbons displaced by said aquifer via said pair of production wells until breakthrough of the interface between the formation fluids and said aquifer at a production well, thereupon ceasing producing formation fluids and injecting into the last mentioned production well an extraneous fluid of predetermined volume to reshape the interface thereat and thereafter continuously injecting an extraneous fluid at a predetermined rate into this well while producing formation fluids including hydrocarbons from said formation via the remaining production well until breakthrough of extraneous driving fluid there, said rate being a percentage of the produced formation fluids.

15. In a method of producing formation fluids including hydrocarbons as defined in claim 14, said extraneous fluid being selected from the group consisting of butane, propane and produced hydrocarbon fluids.

16. In a method of producing formation fluids including hydrocarbons as defined in claim 15, said predetermined volume amounting to about 15 percent of the pattern unit volume. 

1. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation which comprises penetrating said formation with at least three wells substantially in line, a first well, a second well and a third well, the second and third wells being on one side of said first well with said second well closer thereto, injecting an extraneous driving fluid into said formation via said first well to displace fluids including hydrocarbons in said formation toward said second and third wells, producing said formation fluids including hydrocarbons from said formation via said second well, recovering formation hydrocarbon fluids from produced formation fluids, ceasing injecting said extraneous driving fluid and ceasing producing said formation fluids via the production well upon or before suffering breakthrough of said extraneous driving fluid thereat and thereupon injecting a predetermined volume of an extraneous fluid into said formation via said production well suffering breakthrough to reshape the cusp, and thereupon continuously injecting a predetermined portion of the produced formation fluids to provide a dynamic gradient barrier while injecting extraneous driving fluid via said first well and producing formation fluids via said third well until breakthrough of said extraneous driving fluid thereat.
 2. In the method as defined in claim 1, upon breakthrough ceasing injecting said produced formation fluids while maintaining producing said formation fluids including hydrocarbons from said formation via said third well.
 3. In the method as defined in claim 1, continuing injecting produced formatioN hydrocarbon fluids via said well suffering breakthrough first for a predetermined period while maintaining producing via the remaining production well.
 4. In the method as defined in claim 1, said injecting of said extraneous fluid via said production well suffering breakthrough first being a percentage of the pattern unit volume in the amount of about 15 percent, said extraneous fluid being selected from the group consisting of butane, propane and produced hydrocarbon fluids.
 5. In the method of producing formation fluids as defined in claim 1, said three wells in line being part of a thirteen well grouping, wherein the central well of said grouping is an injection well and the remaining grouping wells are production wells arranged equally along the sides and on the diagonals of a quadrilateral, said second and third wells being arranged along a diagonal thereof.
 6. In the method of producing formation fluids as defined in claim 5, simultaneously initiating producing said formation fluids via all of said production wells except the side production wells.
 7. In the method of producing formation fluids as defined in claim 6, ceasing producing from said production wells upon breakthrough thereat and shutting in each one thereafter, and upon ceasing production from the aforementioned production wells, initiating producing from the side wells until breakthrough thereat.
 8. In a method of producing formation fluids including hydrocarbons as defined in claim 1, said wells being part of a direct line drive grouping.
 9. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation which comprises penetrating said formation with at least three wells substantially in line, a first well, a second well and a third well, the second and third wells being on one side of said first well with said second well closer thereto, injecting an extraneous driving fluid into said formation via said first well to displace fluids including hydrocarbons in said formation toward said second and third wells, producing said formation fluids including hydrocarbons from said formation via the second well, recovering formation hydrocarbon fluids from produced formation fluids, ceasing injecting said extraneous driving fluid and ceasing producing said formation fluids upon breakthrough of said extraneous driving fluid at a production well and then injecting an extraneous fluid into said formation via said last mentioned well to reshape the cusp of the interface between said driving fluid and said formation fluids and producing said formation fluids including hydrocarbons from said formation via said third well while injecting said extraneous driving fluid into said formation via said first well and continuously injecting said extraneous fluid into the production well suffering breakthrough until breakthrough of said extraneous driving fluid at said third well.
 10. In the method as defined in claim 9, said injecting of said extraneous fluid via said production well first suffering breakthrough being of predetermined amounts, starting with a percentage of the pattern unit volume for reshaping of the cusp and continuing with a percentage of the produced formation fluids, while producing said formation fluids from said remaining production well to provide a dynamic gradient barrier therebetween.
 11. In the method as defined in claim 9, said extraneous fluid injected via said second well being selected from the group consisting of butane, propane and produced hydrocarbon fluids.
 12. In the method of producing formation fluids as defined in claim 9, said three wells in line being part of a seventeen well grouping, wherein the central well of said pattern is an injection well and the remaining pattern wells are production wells arranged in equal numbers along the sides and on the diagonals of a quadrilateral.
 13. In a method of producing formation fluids as defined in claim 12, producing formation fluids via the wells located on a first diagonal of said grouping and continuing producing therefrom until breakthrough of said extraneous driving fluid occurs at the production well closer to the injection well, thereupon converting said aforementioned diagonal well into an injection well and injecting into said formation via such converted well an extraneous fluid in the amount of 15% of the pattern unit volume, while ceasing injecting said driving fluid, to reshape the cusp of the interface at said converted well, thereupon resuming injecting said driving fluid and producing from the corner well of said first diagonal while continuously injecting said extraneous fluid into said converted well to provide a dynamic barrier therebetween, until breakthrough of said corner well, thereafter shutting in the production wells on said first diagonal and repeating the procedure on the wells on the second diagonal and thereafter producing from the side wells.
 14. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation under the influence of an active aquifer which comprises penetrating said formation with a pair of production wells in line with the direction of advance of said aquifer, producing formation fluids including hydrocarbons displaced by said aquifer via said pair of production wells until breakthrough of the interface between the formation fluids and said aquifer at a production well, thereupon ceasing producing formation fluids and injecting into the last mentioned production well an extraneous fluid of predetermined volume to reshape the interface thereat and thereafter continuously injecting an extraneous fluid at a predetermined rate into this well while producing formation fluids including hydrocarbons from said formation via the remaining production well until breakthrough of extraneous driving fluid there, said rate being a percentage of the produced formation fluids.
 15. In a method of producing formation fluids including hydrocarbons as defined in claim 14, said extraneous fluid being selected from the group consisting of butane, propane and produced hydrocarbon fluids.
 16. In a method of producing formation fluids including hydrocarbons as defined in claim 15, said predetermined volume amounting to about 15 percent of the pattern unit volume. 